Compressors for gas turbine engines comprise alternating annular arrays of stator vanes and rotor blades. The casings of the compressors are manufactured with annular slots into which the vanes are slid. The vanes are mounted on a platform. Each vane is made subject to manufacturing tolerances. These small variations in size become cumulative as the vanes are mounted onto the casing. This means that different sized vanes have to be used to ensure a close circumferential fit.